﻿// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

namespace System.Device.Spi;

/// <summary>
/// The communications channel to a device on a SPI bus.
/// </summary>
public abstract partial class SpiDevice : IDisposable
{
    /// <summary>
    /// Creates a communications channel to a device on a SPI bus running on the current hardware
    /// </summary>
    /// <param name="settings">The connection settings of a device on a SPI bus.</param>
    /// <returns>A communications channel to a device on a SPI bus.</returns>
    public static SpiDevice Create(SpiConnectionSettings settings)
    {
        if (Environment.OSVersion.Platform == PlatformID.Win32NT)
        {
            throw new PlatformNotSupportedException();
        }
        else
        {
            return new UnixSpiDevice(settings);
        }
    }

    /// <summary>
    /// The connection settings of a device on a SPI bus. The connection settings are immutable after the device is created
    /// so the object returned will be a clone of the settings object.
    /// </summary>
    public abstract SpiConnectionSettings ConnectionSettings { get; }

    /// <summary>
    /// Reads a byte from the SPI device.
    /// </summary>
    /// <returns>A byte read from the SPI device.</returns>
    public virtual unsafe byte ReadByte()
    {
        byte value = 0;
        Span<byte> toRead = new Span<byte>(&value, 1);
        Read(toRead);
        return value;
    }

    /// <summary>
    /// Reads data from the SPI device.
    /// </summary>
    /// <param name="buffer">
    /// The buffer to read the data from the SPI device.
    /// The length of the buffer determines how much data to read from the SPI device.
    /// </param>
    public abstract void Read(Span<byte> buffer);

    /// <summary>
    /// Writes a byte to the SPI device.
    /// </summary>
    /// <param name="value">The byte to be written to the SPI device.</param>
    public virtual unsafe void WriteByte(byte value)
    {
        ReadOnlySpan<byte> toWrite = new ReadOnlySpan<byte>(&value, 1);
        Write(toWrite);
    }

    /// <summary>
    /// Writes data to the SPI device.
    /// </summary>
    /// <param name="buffer">
    /// The buffer that contains the data to be written to the SPI device.
    /// </param>
    public abstract void Write(ReadOnlySpan<byte> buffer);

    /// <summary>
    /// Writes and reads data from the SPI device.
    /// </summary>
    /// <param name="writeBuffer">The buffer that contains the data to be written to the SPI device.</param>
    /// <param name="readBuffer">The buffer to read the data from the SPI device.</param>
    public abstract void TransferFullDuplex(ReadOnlySpan<byte> writeBuffer, Span<byte> readBuffer);

    /// <inheritdoc cref="IDisposable.Dispose"/>
    public void Dispose()
    {
        Dispose(true);
        GC.SuppressFinalize(this);
    }

    /// <summary>
    /// Disposes this instance
    /// </summary>
    /// <param name="disposing"><see langword="true"/> if explicitly disposing, <see langword="false"/> if in finalizer</param>
    protected virtual void Dispose(bool disposing)
    {
        // Nothing to do in base class.
    }

    private static readonly byte[] BitReverseTable =
    {
        0x00, 0x80, 0x40, 0xc0, 0x20, 0xa0, 0x60, 0xe0, 0x10, 0x90, 0x50, 0xd0, 0x30, 0xb0, 0x70, 0xf0, 0x08,
        0x88, 0x48, 0xc8, 0x28, 0xa8, 0x68, 0xe8, 0x18, 0x98, 0x58, 0xd8, 0x38, 0xb8, 0x78, 0xf8, 0x04, 0x84,
        0x44, 0xc4, 0x24, 0xa4, 0x64, 0xe4, 0x14, 0x94, 0x54, 0xd4, 0x34, 0xb4, 0x74, 0xf4, 0x0c, 0x8c, 0x4c,
        0xcc, 0x2c, 0xac, 0x6c, 0xec, 0x1c, 0x9c, 0x5c, 0xdc, 0x3c, 0xbc, 0x7c, 0xfc, 0x02, 0x82, 0x42, 0xc2,
        0x22, 0xa2, 0x62, 0xe2, 0x12, 0x92, 0x52, 0xd2, 0x32, 0xb2, 0x72, 0xf2, 0x0a, 0x8a, 0x4a, 0xca, 0x2a,
        0xaa, 0x6a, 0xea, 0x1a, 0x9a, 0x5a, 0xda, 0x3a, 0xba, 0x7a, 0xfa, 0x06, 0x86, 0x46, 0xc6, 0x26, 0xa6,
        0x66, 0xe6, 0x16, 0x96, 0x56, 0xd6, 0x36, 0xb6, 0x76, 0xf6, 0x0e, 0x8e, 0x4e, 0xce, 0x2e, 0xae, 0x6e,
        0xee, 0x1e, 0x9e, 0x5e, 0xde, 0x3e, 0xbe, 0x7e, 0xfe, 0x01, 0x81, 0x41, 0xc1, 0x21, 0xa1, 0x61, 0xe1,
        0x11, 0x91, 0x51, 0xd1, 0x31, 0xb1, 0x71, 0xf1, 0x09, 0x89, 0x49, 0xc9, 0x29, 0xa9, 0x69, 0xe9, 0x19,
        0x99, 0x59, 0xd9, 0x39, 0xb9, 0x79, 0xf9, 0x05, 0x85, 0x45, 0xc5, 0x25, 0xa5, 0x65, 0xe5, 0x15, 0x95,
        0x55, 0xd5, 0x35, 0xb5, 0x75, 0xf5, 0x0d, 0x8d, 0x4d, 0xcd, 0x2d, 0xad, 0x6d, 0xed, 0x1d, 0x9d, 0x5d,
        0xdd, 0x3d, 0xbd, 0x7d, 0xfd, 0x03, 0x83, 0x43, 0xc3, 0x23, 0xa3, 0x63, 0xe3, 0x13, 0x93, 0x53, 0xd3,
        0x33, 0xb3, 0x73, 0xf3, 0x0b, 0x8b, 0x4b, 0xcb, 0x2b, 0xab, 0x6b, 0xeb, 0x1b, 0x9b, 0x5b, 0xdb, 0x3b,
        0xbb, 0x7b, 0xfb, 0x07, 0x87, 0x47, 0xc7, 0x27, 0xa7, 0x67, 0xe7, 0x17, 0x97, 0x57, 0xd7, 0x37, 0xb7,
        0x77, 0xf7, 0x0f, 0x8f, 0x4f, 0xcf, 0x2f, 0xaf, 0x6f, 0xef, 0x1f, 0x9f, 0x5f, 0xdf, 0x3f, 0xbf, 0x7f,
        0xff
    };

    /// <summary>
    /// Reverse the byte
    /// </summary>
    /// <param name="toReverse">The byte to reverse</param>
    /// <returns></returns>
    internal static byte ReverseByte(byte toReverse) => BitReverseTable[toReverse];

    /// <summary>
    /// Reverse the bytes
    /// </summary>
    /// <param name="span">The Span of byte to reverse</param>
    internal static void ReverseByte(Span<byte> span)
    {
        for (int i = 0; i < span.Length; i++)
        {
            span[i] = ReverseByte(span[i]);
        }
    }
}
